Recent advances in the application of colloidal silica have brought an increase in the demand for low sodium colloidal silica products. Producers of electronic chips currently view the presence of sodium as an undesirable contaminant. Their belief is that sodium ions present in the final product result in defective microchips. Thus, manufacturers of electronic components have begun to request that the materials used in manufacturing have lower sodium levels.
The areas of coatings and catalysts also have been an increase in demand for low sodium colloidal silica products. Excessive sodium can lead to unwanted haze or cracking in many coating applications. Sodium has been shown to be detrimental to catalyst behavior by lessening the selectivity and activity of catalysts. In many instances, the presence of sodium leads to total catalyst deactivation.
The following patents teach the production of low sodium silica sols:
Weldes, U.S. Pat. No. 3,239,521 discloses a method of forming soluble sodium free hydroxylated organic quaternary nitrogen silicates. While producing a silica containing compounds substantially free sodium, Weldes does not form a sol and his ratio of quaternary to silica content is high. Another Weldes Patent U.S. Pat. No. 3,326,910 also discloses a method for preparation of amine silicates which are substantially free of alkali metal ions. Again, the silicate used is reacted with an amine and the resulting amine silicate solution is apparently soluble in water.
Yates, U.S. Pat. No. 3,597,248 discloses a method of producing guanidine silicates. Again, the form of the silicate is water soluble and contains a large percentage of the organic amine. A second Yates Patent, U.S. Pat. No. 3,630,954 discloses colloidal silica sols having a high surface are which are stabilized by an organic amine and strong base.
Vossos et al. U.S. Pat. No. 3,582,494 discloses a method for producing alkaline aqueous colloidal silica sols from salt free acidic colloidal sols by treating such acidic sols with at least 0.003% by weight, based on the weight of the silica in such sol, of a salt whose anion is derived from a weak acid and whose ionization constant should not exceed that of carbonic acid in order to stabilize the sol. While Vossos apparently provides to the art a sol containing a low amount of alkali metal, even the alkali metal content which Vossos provides within his sol is deleterious in certain applications.
Rule, U.S. Pat. No. 2,577,484 discloses a process for producing stable silica sols having an SiO.sub.2 to "base" molar ration, expressed as "M.sub.2 O" being from 130:1 to 500:1. Rule also discloses a method for utilizing alkanol amines as a stabilizer.
Schaefer, U.S. Pat. No. 4,054,536 discloses a process producing silica sols free of metal oxides thorough the use of organic amines. Such sols having broad particle size ranges and short stabilities.